EP0362653A1 - Process for the preparation of cathodically depositable self-crosslinking paint binders - Google Patents

Abstract

The invention relates to a process for the preparation of cathodically depositable, self-crosslinking binders for paints, in which process groups which are capable of crosslinking are introduced into the binders by reaction of hydroxyl groups and/or primary and/or secondary amino groups of the binders with diblocked diisocyanates of the general formula <IMAGE> where R is an aliphatic, cycloaliphatic or aromatic radical originating from a diisocyanate, R1 is an aliphatic, cycloaliphatic or aromatic radical originating from a diisocyanate whose NCO groups have predominantly different reactivity, and R2 and R3 are identical or different radicals of NCO-blocking agents, at 70 to 100 DEG C, preferably in the presence of an organic isocyanate-inert solvent.

Description

wobei
R ein von einem Diisocyanat stammender aliphatischer, cycloaliphatischer oder aromatischer Rest,
R₁ ein von einem Diisocyanat, dessen NCO-Gruppen über­wiegend verschiedene Reaktivität aufweisen, stammen­der aliphatischer, cycloaliphatischer oder aromati­scher Rest ist
und
R₂ und R₃ gleiche oder verschiedene Reste von NCO-Blok­kierungsmitteln darstellen,
in die Bindemittel eingeführt werden.The invention relates to a process for the preparation of cathodically depositable, self-crosslinking lacquer binders, according to which crosslinkable groups by reaction of hydroxyl groups and / or primary and / or secondary amino groups of the binders with diblocked triisocyanates of the general formula

in which
R is an aliphatic, cycloaliphatic or aromatic radical derived from a diisocyanate,
R₁ is an aliphatic, cycloaliphatic or aromatic radical derived from a diisocyanate whose NCO groups predominantly have different reactivities
and
R₂ and R₃ represent the same or different residues of NCO blocking agents,
into which binders are introduced.

DE-OS 22 52 536 discloses a process for producing self-crosslinking binders for cathodically depositable electrocoat materials, by means of which the hydroxyl groups of epoxy resin-amine adducts are reacted with partially blocked polyisocyanates. As partially blocked polyisocyanates semi-blocked diisocyanates are used, although individual tri- and tetra-isocyanates are mentioned in a summary in the description. The literature does not provide any information about a method of partially blocking such polyisocyanates in such a way that a monoisocyanate compound is used to a substantial extent.

The half-blocked diisocyanates mentioned are used, as described in many references, to introduce reactive groups into polymers which are used as self-crosslinking, thermosetting paint binders, particularly in water-dilutable electrocoat materials. Since only one crosslinking group is introduced in each case when using the customary semi-blocked diisocyanates, adequate crosslinking of the polymers can hardly be achieved in this way.

It has now been found that an improvement in the chemical and mechanical properties of the films of cathodically depositable and essentially self-crosslinking varnish binders is possible if the crosslinking component is in the form of a diblocked triisocyanate, which has a structure corresponding to the initially mentioned formula, in introduces the binder.

wobei
R ein von einem Diisocyanat stammender aliphatischer, cycloaliphatischer oder aromatischer Rest,
R₁ ein von einem Diisocyanat, dessen NCO-Gruppen über­wiegend verschiedene Reaktivität aufweisen, stammen­der aliphatischer, cycloaliphatischer oder aromati­scher Rest ist
und
R₂ und R₃ gleiche oder verschiedene Reste von NCO-Blok­kierungsmitteln darstellen,
bei 70 bis 100°C, vorzugsweise in Gegenwart eines orga­nischen isocyanat-inerten Lösemittels, in die Bindemit­tel einführt.The present invention accordingly relates to a process for the preparation of paint binders which can be deposited cathodically and self-crosslinking at elevated temperature, which is characterized in that the crosslinkable groups are reacted by reaction of hydroxyl groups and / or primary and / or secondary Amino groups of the binders with diblocked triisocyanates of the general formula

in which
R is an aliphatic, cycloaliphatic or aromatic radical derived from a diisocyanate,
R₁ is an aliphatic, cycloaliphatic or aromatic radical derived from a diisocyanate whose NCO groups predominantly have different reactivities
and
R₂ and R₃ represent the same or different residues of NCO blocking agents,
at 70 to 100 ° C, preferably in the presence of an organic isocyanate-inert solvent, introduced into the binder.

The invention further relates to the use of the paint binders prepared in this way for the formulation of cathodically depositable electrocoat materials.

All resins which have a sufficient number of isocyanate-reactive groups can be used as the base resins for the reaction with the diblocked triisocyanates according to the invention, so that on the one hand the reaction with the monoisocyanate compound can take place and on the other hand such groups are available for the crosslinking reaction. For your one As a water-thinnable electrocoat binder, the base resins must have a corresponding number of protonatable groups, provided that these groups are not introduced in whole or in part via corresponding isocyanate compounds.

Products of this type which can be used as base resins in the sense of the present invention are described in large numbers in the literature. These are mainly epoxy resin amine adducts of various structures, as well as acrylic or polydiene (co) polymers, modified phenol ethers, polyesters, polyethers and the like. the like

Due to the extensive literature, a more detailed description of the manufacturing processes for these resins does not appear to be necessary. The preferred types are exemplified in the exemplary embodiments.

The diblocked triisocyanates used according to the invention are prepared by reacting 1 mol of a fully blocked diisocyanate with 1 mol of an unblocked diisocyanate, the NCO groups of which predominantly have different reactivities, at 70 to 120 ° C., optionally in the presence of a catalyst. It has been shown that if the reaction temperature is chosen correctly, only one NCO group of the unblocked diisocyanate is consumed and the free NCO group of the resulting allophanate compound does not react even if the reaction time is prolonged or the product is stored. The maximum reaction temperature must accordingly be chosen so that there is still no substantial reaction of the free NCO group of the product and / or no substantial elimination of the blocking agent.

Any diisocyanate can be used for full blocking, provided its NCO groups are accessible for blocking and unblocking at temperatures between 120 and 200 ° C.

Compounds whose NCO groups have different reactivities must be used as diisocyanates for the reaction with the fully blocked diisocyanate to achieve uniform products. Examples of commercially available products of this type are isophorone diisocyanate or 2,4-tolylene diisocyanate. When using technical isomer mixtures, such as those found in many commercial products of tolylene diisocyanate (80% 2,4- and 20% 2,6-TDI), deviations are to be expected, but these are usually of no significant importance for further use.

The compounds known from the literature and having a reactive hydrogen atom are used as blocking agents (see, for example, “Methods of Organic Chemistry”, (HOUBEN-WEYL), vol. 14/2, pages 61-70, G. Thieme-Verlag, Stuttgart 1963). According to the definition, the blocking agents have to be removed at a temperature which is useful in practice with the intermediate reformation of the isocyanate group.

Examples of blocking agents are
Monohydroxyl compounds, such as alkanols, glycol monoethers, hydroxyalkyl acrylates, dialkylalkanolamines, ketoximes,
Lactams, such as epsilon-caprolactam or delta-valerolactam,
CH-active compounds such as acetylacetone, acetoacetic ester or malonic ester derivatives,
aliphatic amines, such as 2-ethylhexylamine, dibutylamine, dimethyl- or diethylaminopropylamine.

Mixtures of different blocking agents can of course also be used. When using suitable amino alcohols, such as the dialkylalkanolamines mentioned, or of primary tert. Amines are simultaneously introduced by the blocking agent into a protonatable group that splits off during curing.

In the preparation of the monoisocyanate compounds used according to the invention, the diisocyanate is reacted at 30 to 50 ° C. with the blocking agent in such a ratio that both NCO groups are blocked. The fully blocked diisocyanate is then reacted with an equimolar amount of a diisocyanate which has differently reactive NCO groups at 70 to 120 ° C to the monoisocyanate. If necessary, the reaction can be accelerated by basic catalysts, such as triethylamine or a basic blocking agent. The addition of the diisocyanate is advantageously started at approximately 70 ° C. and the temperature is increased in accordance with the course of the reaction. At the maximum temperature used, neither the second NCO group reacts nor the blocking agent is split off. Under the given conditions, the reaction comes to a standstill when the diisocyanate is converted on one side.

The reaction of the monoisocyanate compound with the base resin takes place at 70 to 100 ° C. until the isocyanate groups have been completely consumed, advantageously in Presence of an organic, isocyanate-inert solvent, such as the monoethylene glycol monoethyl ether acetate or an ethylene glycol diether. Optionally, the binder produced according to the invention is combined with other resins.

The formulation, production and processing of cathodically depositable electrocoat materials from the binders produced according to the invention is carried out by the customary methods known to the person skilled in the art. If necessary, the lacquers can also be processed in a conventional manner by spraying, dipping or flooding.

The following examples illustrate the invention without restricting its scope. Unless otherwise stated, all parts or percentages relate to units of weight. The NCO value indicates the amount of free isocyanate groups in% by weight.

The following abbreviations are used in the examples (unless otherwise explained in the text):
TDI / 80 tolylene diisocyanate (commercially available mixture of isomers; 80% 2.4% 20% 2,6-TDI)
2,4-TDI 2,4-tolylene diisocyanate (technical)
TMHMDI trimethylhexamethylene diisocyanate
IPDI isophorone diisocyanate
EH 2-ethylhexanol
BG monoethylene glycol monobutyl ether
DEOLA diethylethanolamine
BOX butanone oxime
DEAPA diethylaminopropylamine
AC acetylacetone
TEA triethylamine
CL epsilon-caprolactam
DMBA dimethylbenzylamine
DGDME diethylene glycol dimethyl ether
EGAC monoethylene glycol monoethyl ether acetate
EEW epoxy equivalent weight
ES acetic acid
AS formic acid
DBTL dibutyltin dilaurate
POCT lead octoate (31% Pb)

(A) Preparation of the diblocked triisocyanate compounds (MIC)

The diisocyanate (I) (1 mol) intended for full blocking is placed in a suitable reaction vessel and the blocking agent (2 mol) is added continuously at 30 to 40 ° C. with cooling.

The temperature is then maintained until all NCO groups have completely converted. After heating to 70 ° C., optionally after adding a catalyst, the diisocyanate (II) (1 mol) intended for the further reaction is slowly added. The temperature is slowly increased to the intended maximum temperature. When the theoretical NCO value for the monoisocyanate is reached, the temperature is held for a further 15 minutes. The product can be processed immediately or stored at room temperature.

When using isocyanates with different reactive NCO groups as diisocyanate (I) and as diisocyanate (II), the reaction can also be carried out in such a way that the blocking agent (2 mol) is placed in the reaction vessel and the first half (1 mol) of the Diiso cyanate is added at 30 to 40 ° C. The second half (1 mol) of the diisocyanate is then added and the mixture is reacted.

The quantitative ratios, reaction conditions and characteristic values are summarized in Table 1 below. Table 1 MIC Diisocyanate (I) Tle (1 mol each) Blocking agent Tle (mol) Diisocyanate (II) Tle (1 mol each) % Catalyst by weight Max Reaction Temp. ° C molar mass NCO theor. Value found 1 174 TDI / 80 260 (2.0) EH 222 IPDI 0.5 TEA 120 656 6.4 6.35 2nd 210 TMHMDI 177 (1.5) BG 174 2,4-TDI - 105 620 6.8 6.7 59 (0.5) DEOLA 3rd 222 IPDI 174 (2.0) BOX 222 IPDI - 110 618 6.8 6.8 4th 174 TDI / 80 234 (1.8) EH 174 2,4-TDI - 105 608 6.9 6.9 26 (0.2) DEAPA 5 210 TMHMDI 118 (1.0) BG 222 IPDI 0.8 TEA 120 663 6.3 6.2 113 (1.0) CL 6 174 TDI / 80 130 (1.0) EH 222 IPDI - 110 643 6.5 6.5 117 (1.0) DEOLA 7 174 TDI / 80 200 (2.0) AC 174 2,4-TDI 0.5 DMBA 120 548 7.7 7.6 8th 210 TMHMDI 177 (1.5) BG 174 TDI / 80 - 110 620 6.1 5.4 59 (0.5) DEOLA

(B) Production of base resins (BH)

• (BH 1) 500 parts of an epoxy resin based on bisphenol A (EEW approx. 500) are dissolved in 214 parts of DGDME and at 110 ° C with 83 parts of a half ester of phthalic anhydride and 2-ethylhexanol in the presence of 0.5 g of triethylamine Catalyst reacts up to an acid number of less than 3 mg KOH / g. Then 120 parts of an NH-functional oxazolidine from aminoethylethanolamine, 2-ethylhexyl acrylate and formaldehyde, and 26 parts of diethylaminopropylamine are added and the mixture is converted at 80 ° C. to an epoxy value of practically 0. The mixture is diluted with 200 parts DGDME (hydroxyl number approx. 180 mg KOH / g).
• (BH 2) A novolak resin prepared in a known manner from 228 parts of bisphenol A, 220 parts of nonylphenol and 59 parts of paraformaldehyde (91%), which is etherified with 174 parts of propylene oxide, is dissolved in 200 parts of DGDME. The product contains 3 moles of aliphatic hydroxyl groups.
• (BH 3) 228 parts of bisphenol A (1 mol) are reacted with 260 parts of diethylaminopropylamine (2 mol) and 66 parts of paraformaldehyde 91% (2 mol) in the presence of 131 parts of toluene as an azeotropic entrainer until 42 parts of water of reaction are separated off. The product contains 2 moles of secondary amino groups.
• (BH 4) 950 parts of an epoxy resin based on bisphenol A (EEW approx. 475) are mixed in 430 parts DGDME with 105 parts (1.0 mol) diethanolamine and 65 parts (0.5 Mol) of diethylaminopropylamine at 60-80 ° C. until all epoxy groups have been completely consumed (hydroxyl number approx. 300 mg KOH / g).
• (BH 5) 55% solution in EGAC of a polyester made from 0.5 mol isophthalic acid, 1.0 mol trimethylolpropane, 0.7 mol 1,6-hexanediol (acid number below 5 mg KOH / g, hydroxyl number approx. 280 mg KOH / G.

(C) Production of the paint binders according to the invention

• Example 1: In a reaction vessel equipped with a stirrer, thermometer and addition vessel, 1143 parts of the base resin (BH 1), corresponding to 729 parts of solid resin, are mixed with 312 parts of the isocyanate compound (MIC 1) at 70 ° C. and slowly at up to 100 ° C. increasing temperature up to an NCO value of 0. The mixture is diluted to a solids content of 60% with DGDME. The product has an amine number of 64 mg KOH / g.
• Example 2: In the same way as in Example 1, 834 parts (BH 2), corresponding to 634 parts solid resin, are reacted with 643 parts (MIC 6) and diluted to a solids content of 62% with DGDME. The batch is further mixed with an amount of (BH 4) corresponding to 547 parts of solid resin. The product has an amine number of 61 mg KOH / g.
• Example 3: In the same way as in Example 1, 1550 parts (BH 4), corresponding to 1120 parts solid resin, are reacted with 603 parts (MIC 5) and diluted with DGDME to a solids content of 60%. The product has an amine number of 65 mg KOH / g.
• Example 4: In the same way as in Example 1, 545 parts of the 55% solution of (BH 5) are reacted with 200 parts (MIC 6) and diluted with EGAC to a solids content of 65%. The batch is further mixed with an amount of (BH 1) corresponding to 333 parts of solid resin. The product has an amine number of 72 mg KOH / g.
• Example 5: In the same way as in Example 1, 643 parts (BH 3), corresponding to 512 parts of solid resin, are reacted with 1216 parts (MIC 4) and diluted with DGDME to a solids content of 60%. After adding 190 parts of a bisphenol A diglycidyl ether (EEW 190) and 186 parts of 2-ethylhexylglycidyl ether, the mixture is reacted at 100 ° C. for a further 3 hours. The product has an amine number of 78 mg KOH / g.
• Example 6: In the same way as in Example 1, 1143 parts (BH 1), corresponding to 729 parts solid resin, are reacted with 243 parts (MIC 3) and diluted with DGDME to a solids content of 65%. The product has an amine number of 69 mg KOH / g.
• Example 7: In the same way as in Example 1, 834 parts (BH 2), corresponding to 634 parts solid resin, are reacted with 930 parts (MIC 2) and diluted with DGDME to a solids content of 65%. The product has an amine number of 27 mg KOH / g.
• Example 8: In the same way as in Example 1, 1550 parts (BH 4), corresponding to 1120 parts solid resin, are reacted with 548 parts (MIC 7) and diluted with DGDME to a solids content of 65%. After 548 parts (BH 2), corresponding to 417 parts of solid resin, have been mixed in, the product has an amine number of 54 mg KOH / g.
• Example 9: corresponds to example 7, but instead of 930 parts (MIC 2) 930 parts (MIC 8) are used.

Manufacture of test paints

According to the information in the following Table 2, the resins are mixed with the acid and the catalyst and diluted with water to the stated solids content. The clear coat is then mixed with the pigment paste. After a homogenization time of 24 hours, zinc-phosphated steel sheets are coated with the test varnishes and baked at the temperature given in Table 2.

With a film thickness of 23 ± 2 µm, the sheets have a salt spray resistance (ASTM-B 117-64; detachment at cross-cut under 2 mm) of more than 1000 hours.

The pigment paste used is produced in the following way:

100 parts of solid resin of the paste binder according to Example 2 of AT-PS 380 264 are added after adding 5 parts of a wetting agent based on an acetylene alcohol (calculated as solid substance, used as a 25% solution in ethyl glycol), with 24 parts of lactic acid (5 n) and deionized water transferred to a 15% aqueous clear coat. After adding 24 parts of carbon black, 1104 parts of titanium dioxide and 72 parts of basic lead silicate, grinding takes place in a laboratory mill. The resulting pigment paste has a solids content of approx. 51% and a pigment / binder ratio of 12: 1. Table 2 Paint no. Tle binder solution (from example) N ⁽¹⁾ K ⁽²⁾ Clear coat% PP ⁽³⁾ P / B ⁽⁴⁾ EBT ⁽⁵⁾ 1 167 (1) 40 AS 0.8 DBTL 13 106 0.5: 1 180 2nd 161 (2) 50 AS 1.0 DBTL 15 106 0.5: 1 160 3rd 167 (3) 45 ES 1.0 POCT 15 85 0.4: 1 150 4th 154 (4) 45 AS 0.6 DBTL 15 106 0.5: 1 180 5 167 (5) 40 AS 0.8 DBTL 12 127 0.6: 1 160 6 154 (6) 45 ES - 15 64 0.3: 1 150 7 154 (7) 60 AS 0.5 POCT 15 106 0.5: 1 160 8th 167 (8) 50 ES 1.0 POCT 14 85 0.4: 1 180 9 154 (9) 60 AS 0.5 POCT 15 106 0.5: 1 160 (1) Neutralizing agent: mmol of acid per 100 g of solid resin (2) Catalyst:% by weight of metal based on solid resin (3) Pigment paste: amount as a solid (4) Pigment-binder ratio in the dip coating (5) Baking temperature for the deposited paint films.

Claims (2)

1. A process for the preparation of cathodically depositable and self-crosslinking lacquer binders, characterized in that the crosslinkable groups by reaction of hydroxyl groups and / or primary and / or secondary amino groups of the binders with diblocked triisocyanates of the general formula

in which
R is an aliphatic, cycloaliphatic or aromatic radical derived from a diisocyanate,
R₁ is an aliphatic, cycloaliphatic or aromatic radical derived from a diisocyanate whose NCO groups predominantly have different reactivities
and
R₂ and R₃ represent the same or different residues of NCO blocking agents,
at 70 to 100 ° C, preferably in the presence of an organic isocyanate-inert solvent, introduced into the binder. 2. Use of the self-crosslinking paint binder according to claim 1 for the formulation of cathodically depositable electrocoat materials.